To impart water- and weather-resiatant properties to wood simultaneously with improvement of its physico-mechanical properties use is made of impregnation with synthetic resins including both monomers and oligomers, followed by polycondensation effected by the thermochemical method.
In the world practice for this purpose use is made of impregnation compositions based on phenol-formaldehyde resins. The basic formulations have been developed by Koppers Co., Diversified Wood Products Inc., Wayerhaeuser Co., Dow Chemical Co.
The principle of all these formulations resides in carrying out polycondensation of a monohydric phenol with formaldehyde for the preparation of oligomers curing with temperature or when exposed to heat in the presence of an additional amount of formaldehyde. For example, in U.S. Pat. No. 4,031,276 to Sumitomo Durez Co. for impregnation of wood use is made of a solution of a resol-type resin in a mixture of acetone and methanol. The company also has a number of processes based on the use of various starting compounds for the impregnation composition and different types of curing catalysts.
Wayerhaeuser Co. suggests, in U.S. Pat. No. 3,284,231. an impregnation composition containing methylolphenol, free formaldehyde and a weak organic acid.
In further developments, e.g. in U.S. Pat. No. 3,968,276 an additional use is made of products increasing fire-resistance of wood.
U.S. Pat. No. 3,159,503 to Koppers Co. teaches the use, as an impregnation composition, of a solution of a dicyanodiamide, orthophosphoric acid and free formaldehyde. Swedish Pat. No. 405,218 the same company suggests an impregnation composition based on monomethyloldicyanodiamide, melamine and orthophosphoric acid.
In U.S. Pat. No. 3,519,476 to Dow Chemical Co. use is made of an impregnation composition produced by interaction of an alkylphenol with an aliphatic or a cycloaliphatic amine in an acidic medium. After impregnation the wood is treated with ammonia at a temperature of from 85.degree. to 150.degree. C.
In the USSR there have been successfully employed impregnation compositions based on phenolic alcohols and a number of modifications thereof, e.g. a solution of phenyltrichlorosilane in acetone (cf. USSR Inventor's Certificate No. 390950), urea-formaldehyde resin (USSR Inventor's Certificate No. 575218), kerosene-gasoil fraction of oil (USSR Inventor's Certificate No. 763093), maleic anhydride (USSR Inventor's Certificate No. 620373).
Also known in the art is the use of an impregnation composition based on carbamidoformaldehyde resins with the addition of furan compounds and ammonium chloride for curing of the composition (cf. USSR Inventor's Certificate No. 414096).
According to USSR Inventor's Certificate No. 601162 use is made of an impregnation composition based on a mixture of caprolactam and higher fatty acids with the stage of keeping the wood in a solution of iron-ammonium alum and hydrogen peroxide prior to impregnation.
The life time of impregnation compositions based on polycondensation resins is extended in the presence of amino alcohols (cf. USSR Inventor's Certificate No. 656833).
A disadvantage of modification of wood by means of phenolic alcohols and phenol-formaldehyde oligomers resides in a non-uniform impregnation, corrugation and cracking of wood. Furthermore, the above-described impregnation compositions are instable, contain free formaldehyde and can be cured at a high temperature.
The prior art composition closest to that of the present invention as regards its subject matter and the result obtained is the impregnation composition according to U.S. Pat. No. 3,832,251 comprising monomeric resorcinols and a donor of formaldehyde-dimethylolurea in an aqueous solution of ethanol.
This impregnation composition is prepared by mixing monomeric resorcinols with an aqueous-ethanol solution of dimethylolurea.
The above-described impregnation composition according to U.S. Pat. No. 3,832,251 has, apart from the positive characteristics, certain disadvantages such as:
1. Due to the presence of free formaldehyde (up to 2%) in the impregnation composition and, hence, in the modified wood in the amount determined by equilibrium of the reaction of the formation and decomposition of dimethylolurea there are encountered sanitary-hygienic difficulties in the use of the composition and subsequent processing of ski blanks. PA0 2. A low stability of the impregnation composition hinders elevation of the drying temperature above 50.degree. C. and preparation of a composition with a content of dry solids above 30% (50% content of the dry solids is attained only upon the preparation of the composition in small amounts). PA0 3. Due to a low stability of the aqueous-ethanolic solution of dimethylolurea, the latter is prepared directly in situ, i.e. at the site of application thereof, wherefore it is impossible to carry out centralized preparation of the impregnation composition. PA0 4. Brittleness of the wood modified by means of this impregnation composition hinders its mechanical treatment in the manufacture of the ski edge and lower layer.